Ok, if she is not in milk she is underconditioned. With a good deworming and good food she should gain weight quickly.
Here is a doe that I bought back from an individual who purchased her from my parents in 2007.
This photo was taken in March 2011, shortly after I brought her home. She is very underweight in this picture.
This photo was taken in June 2011, 2 1/2 months after being on my feeding program. She is at a good weight in this photo, and new, healthy hair is starting to come in under the rough unhealthy coat that she had before.
This photo was taken in September 2011, nearly 6 months after I purchased her.
You see how quickly she gained weight, and in the third picture is actually slightly overconditioned. Dry mature does do not have many demands on their bodies so can gain weight easily. In fact, this doe spontaneously came into milk with good feed. I only milked enough to prevent overbagging because she was never trained to the milk stand and I didn't want to mess with training her to the milk stand without having maternal hormones to help! She is due to kid at the end of February or the beginning of March (depending on whether or not she goes over her due date) and will be trained to the milk stand then.